Method of making a porous laminated metal-bonded cutting wheel

ABSTRACT

A COOL RUNNING ABRASIVE CUTTING TOOL HAVING A WORKING SURFACE COMPRISING A LAYER OF DIAMOND PARTICLES INCLUDED IN A HEAT-CONDUCTIVE MATRIX AND A HEAT-DISSIPATING REGION IMMEDIATELY SUBJACENT THE WORKING SURFACE. THE HEATDISSIPATING REGION IS COMRISED OF A HIGHLY POROUS MATERIAL HAVING A MACRO-POROSITY PROFILE, AN EXTENDED INTERNAL HEAT TRANSFER SURFACE AREA AND PREFERABLY IS FORMED FROM A METAL HAVING A THERMAL CONDUTIY COEFFIECNT OF AT LAST ABOUT 0.05 G,-CAL. (SEC.)(CM2)(*C. CM.), A PARTICULAR ELCTROPLAST DIAMOND PERIPHERAL WHEEL IN DISCLOSED.

y 8, 1974 H. w. FERCHLAND METHOD OF MAKING A POROUS LAMINATEDMETAL-BONDED CUTTING WHEEL Original Filed Aug; 9, 1968 5 Sheets-Sheet 1(f /9.5 INVENTOR. Harv/a [1/ field/and dy/aw 4/44 5 ATTORNEf H. W.FERCHLAND May 28, 1974 METHOD OF MAKING A POROUS LAMINATED METAL-BONDEDCUTTING WHEEL 5 Sheets-Sheet 2 Original Filed Aug. 9. 1968 INVENTOR.Harold (l ism/Hand ATTORNEY y 1974 H. w. FERCHLAND 3,813,230

.METHOD OF MAKING A POROUS LAMINATED METAL-BONDED CUTTING WHEEL OriginalFiled Aug. 9, 1968 I 5 Sheets-Sheet 3 INVENTOR.

Ham/d [a jam/21am BY W ,4 W

ATTORNEY H. W. FERCHLAND METHOD OF MAKING A POROUS LAMINATEDMETAL-BONDED CUTTING WHEEL Original Filed Aug. 9, 1968 TEMPERATURE FTEMPERAT RE 'F AIR COOLED TC DEPTH .025 IN.

RESIN BONDED CU. SOLID WHEEL FEED INTO SAMPLE BLOCK (INCHES) NI. POROUSWATERICOOLED TC .062 IN.

CU. POROUS .OOI WHEEL FEED INTO SAMPLE BLOCK '(mcHEs) TEMPERATURE 'F 5Sheets-Sheet 4 WHEEL FEED INTO SAMPLE TEMPERATURE 'F N BLOCK (INCHES)AIR COOLED TC DEPTH NI.POROUS .062 IN.

CU. POROUS WHEEL FEED INTO SAMPLE BLOCK (INCHES) ATTORNEY May 23, 1914H. w. FERCHLAND METHOD OF HAKING A POROUS LAMINATED METAL'BONDED CUTTINGWHEEL 5 Sheet-Sheet 5- Original Filed Aug. 9, 1968 AIR COOLED TC DEPTH-'o.os2 IN.

HEAT DISSIPATING REGION-SURFACE AREA INF/INS WATER COOLED TC DEPTH 0.062IN.

HEAT DISSIPATING REGION-SURFACE AREA IN /1N jay/7 AIR COOLED BLOCKTEMPERATURE RESlN-BONDED WHEEL POROUS WHEEL RESIN-BONDED |9 M M 4 n W n,d 0 W J 5 E m LmS w m .m Nv .5F(I\ wLK 4..HL H we ATTORNEY United StatesPatent 3,813,230 METHOD OF MAKING A POROUS LAMINATED METAL-BONDEDCUTTING WHEEL Harold W. Ferchland, Troy, Mich., assignor to GeneralMotors Corporation, Detroit, Mich.

Apphcation July 31, 1969, Ser. No. 850,314, now Patent No. 3,641,718,which is a continuation of abandoned application Ser. No. 751,479, Aug.9, 1968. Divided and this application Oct. 27, 1971, Ser. No. 193,226

Int. Cl. B24d 7/10 US. Cl. 51-297 2 Claims ABSTRACT OF THE DISCLOSURE Acool running abrasive cutting tool having a working surface comprising alayer of diamond particles included in a heat-conductive matrix and aheat-dissipating region immediately subjacent the working surface. Theheatdissipating region is comprised of a highly porous material having amacro-porosity profile, an extended internal heat transfer surface areaand preferably is formed from a metal having a thermal conductivitycoefficient of at least about 0.05 g.-cal./(sec.) cm. C./cm.). Aparticular electroplated diamond peripheral wheel is disclosed.

This application is a division of Ser. No. 850,314, filed July 31, 1969now Pat. No. 3,641,718 which is a continuation of Ser. No. 751,479 filedAug. 9, 1968 and now abandoned.

This invention relates generally to grinding or abrasive cutting tools.Though the invention will be described primarily in terms ofelectroplated diamond peripheral wheels, the principles involved hereinare applicable to other diamond wheels and abrasive cutting tools suchas cut-off wheels, standard plain wheels, contoured wheels, plain andtaper cup wheels, internal wheels, mounted wheels, glass-edging wheels,and masonry wheels. Accordingly, the benefits of this invention can beachieved on equipment such as internal and external grinders, toolgrinders, optical grinders, masonry saws, surface grinders, centerlessgrinders, chip grinders, spline grinders, etc.

In prior art there are generally two types of grinding wheels. The firstof these are the ceramic type which are generally high-mass wheelsmolded into a fused cellular structure by bonding particles, such as A10 together in a glass matrix. Some of these wheels, e.g., such asdisclosed in Harrington 2,470,350, permit a limited flow or percolationof coolant through the wheel due to the formation of some microsizedpassages and pores in the wheel during its manufacture. However, inwheels of this type most of the coolant is concentrated near the sidesof the wheel with only a limited amount actually passing through thewheel. Wheels of this type are generally speed limited in that theycannot withstand the destructive forces of high rotational speeds andthe stresses of high-speed grinding. Regardless, increasing the wheelspeed induces more heat into the wheel and the workpiece. The inducedheat shortens the wheels life and causes workpiece disruptive effectssuch as surface crazing, high surface stress swelling, and bulging,among others. The second type of grinding wheel is the solid wheel. Thistype of wheel is typically formed of a solid metal (e.g., aluminum) andhas an abrasive working surface. Metal-bonded diamonds or diamonds heldin a phenolic resin may form the working surface. The solid wheels arequite strong and accordingly have a higher speed capability than thefirst-mentioned wheels. Though higher speeds are possible, from astrength standpoint, high speeds induce excessive heat into both theworkpiece and the wheel. As more heat is generated under continuousoperation the temperature builds in both the ice wheel and the workpieceuntil, in the case of the resinbonded wheels, the bond is destroyed. Inthe metal-bonded wheels, the rising temperature causes swelling of boththe wheel and the workpiece which, if excessive, causes damage to thewheel, to the workpiece and to the grinding machine. It has notheretofore been possible to remove the heat generated at theworkpiece-wheel interface at a sufiicient rate to substantially increasethe cutting rates of the presently commercially available wheels. In asense then, it might be said that such commercial wheels areheat-limited tools. That is to say, there is an upper limit of cuttingrate which cannot be exceeded owing to the prior arts inability todissipate the generated heat.

It is an object of this invention to overcome both the speed-limited andheat-limited shortcomings of the prior art wheels by providing a wheelwhich not only cuts faster and cooler than any wheel known heretofore,but which uses less power to do so while at the same time having alonger useful life.

This and other objects of this invention will become more apparent fromthe detailed description which follows.

Wheels according to this invention have a working surface comprising alayer of diamonds included in a porous heat conductive matrix and aheat-dissipating region or core subjacent that working surface. Diamond,unlike other abrasives, have the distinction of not only havingexcellent cutting capabilities but also of having an exceptionally highthermal conductivity, i.e., about five times that of copper. Theheat-dissipating region is comprised of a material which is replete withmacro-sized coolant flow passages to permit the flooding of the workingsurface with macro-volumes of coolant flowing to it through theheat-dissipating region. Desirably, the heatdissipating region and thematrix for holding the diamonds are comprised of metals which have athermal conductivity coefficient of at least about 0.05 g.-cal./(sec.)(cm. 'C./crn.) and preferably at least about 0.1 g.- cal./(sec.) (cm.C./cm.). The heat-dissipating region has a porosity profile such thatthe interstitial voids, which form the coolant flow passages, areexposed to an extended heat transfer surface area. By porosity profileis meant the nature, configuration, size and distribution of the cellsor voids which form the coolant flow passages and make up the voidvolume of the heat-dissipating region (e.g., cells per lineal inch). Theexpression macrosized is intended to define sufiiciently large passagesto permit the macro-volume flow of coolant as distinguished from thelow-volume percolation of coolant through micro-porous and/orsubstantially closed cell structures having only capillary sizedpassages. The entire wheel may be constructed of the same material asthe heatdissipating region. When the entire wheel is so constructed,then only that portion immediately subjacent the working surfacefunctions as the heat-dissipating region. When it is so constructed,additional benefits are obtained, including a weight reduction whichcontributes to a savings in power consumption. In its most preferredform the heat-dissipating region is comprised of a porous metal, such ascopper, which has a thermal conductivity coeflicient of about 0.9g.-cal./(sec.)(cm. C./cm.). Other metals and alloys though, such asnickel, iron, aluminum, brass, magnesium, etc., may advantageously beused. In this regard, it has been observed that as the thermalconductivity and the heat transfer surface area of the heat-dissipatingregion increases, the workpiece takes up less heat and the wheel runscooler under sustained cutting conditions. This is especially the casewhere a poor coolant, such as air, is used. As the quality of thecoolant improves, the heat transfer surface area can be reduced. Byrapidly removing the heat generated, the

workpiece and the wheel can be kept below their respective disruptivetemperatures.

FIG. 1 is a side view in the radial direction of the wheel shownpartially in section in FIG. 2.

FIG. 2 is an enlarged partially sectioned front view taken in thedirection 22 of the wheel shown in FIG. 1.

FIG. 3 is a partial front view in the axial direction of another wheelaccording to this invention.

FIG. 4 is a sectioned side view taken in the direction 4-4 of the wheelshown in FIG. 3.

FIG. 5 is an enlarged portion of the sectioned side view of FIG. 4.

FIG. 6 is a partial front view in the axial direction of another wheelaccording to this invention.

FIG. 7 is a sectional side view in the direction 77 of the wheel shownin FIG. 6.

FIG. 8 is an enlarged portion of the sectioned side view shown in FIG.7.

FIG. 9 is a partially sectioned perspective view of another wheelaccording to this invention.

FIG. 10 is a partially sectioned perspective view of a polishing discaccording to this invention.

FIG. 11 is a partially sectioned perspective view of another wheelaccording to this invention.

FIGS. 12 and 13 graphically compare the temperature of the workpiece asa function of the wheel feed, the thermal conductivity and the porosityof several diamond wheels.

FIGS. 14 and 15, under different conditions from FIGS. 12 and 13,graphically compare the temperature of the workpiece as a function ofthe wheel feed, the thermal conductivity and the porosity of severaldiamond wheeels.

FIGS. 16 and 17 graphically compare the temperature of the workpiece atdifferent depths of cut as a function of the extended heat transfersurface area available for convective heat removal from theheat-dissipating region of the various porous diamond wheels within thescope of this invention.

FIG. 18 graphically compares the temperature, at different radialdepths, of several wheels having different heat transfer surface areasradially inboard of the cutting surface.

FIG. 9 graphically compares, at different depths of cut, the workpiecetemperature when cut with a solid, prior art diamond wheel and a porousdiamond wheel of this invention.

FIGS. 1 and 2 disclose one embodiment of a grinding wheel according tothis invention. The wheel 2 is comprised of side plates 6 which areseparated one from the other by a series of pleated metal ribbonsdesignated as 4a, 4b, 4c and 4d. The side plates 6 are bonded, as bybrazing, to the pleated ribbons. As best shown in FIG. 2, the metalcontent of the wheel can be varied in the radial direction by merelychanging the number of pleats per unit length, which are to be placedbetween the side plates 6. The overall weight of the wheel, itsstrength, and its heat-dissipating characteristics can be controlled inthis manner. The ribbon immediately adjacent the wheels periphery, i.e.,4a, serves as the principal heat dissipating layer. A number of holes 8are provided in the side plates 6 and are generally positioned radiallyinward of the wheel. These holes 8 permit the introduction of a coolant,such as water, into the interstices of the wheel during machining. Bycentrifugal action the coolant flows radially outward toward the workingsurface 12. The side plates 6 generally restrict the flow of coolantthrough the wheel and prevent its loss through the face of the wheel.The hub of the wheel 10, in this embodiment, may be any convenientstructure and is not considered to be an integral part of thisinvention. The peripheral portion of the wheel 2 is the wheels workingsurface 12 and is a coating of electrodeposited diamonds. Such coatingsresult from the codeposition of diamonds with a metal electrodepositsuch that the diamonds are included in the electrodeposited metal (e.g.,nickel) which functions as a retaining matrix for the diamonds. Theworking surface 12 is represented in this, and the other drawings, as adistinct layer since it has some finite thicknes, however small.Stippling is intended to show particles. The use of the expressionworking surface hereafter is intended to include the distinct layer,whatever its thickness.

FIGS. 3, 4 and 5 de ict a preferred embodiment of this invention. Inthis embodiment, the wheel 14 is comprised of a number of lamina of wirescreen 16. As best shown in FIGS. 4 and 5, the screens are aligned,stacked and brazed together at the joints 24 where the respectivescreens contact one another. As will be discussed hereinafter, it ispreferred to first corrugate the screens. The respective screen laminaare angularly offset one from the other, as by rotating each screen at adifferent angle about the axis of the center of the wheel. The wheel isprovided with a hub, not shown. Before the hub is attached to the wheel,it is desirable to reinforce the central portion of the wheel. Thisreinforcement is accomplished by impregnating an approximately one inchannulus about the center hole with a thermosetting liquid 22. Thisfeature will be discussed in more detail hereinafter. The wheel has aworking surface 20 which is comprised of an abrasive layer 18 ofelectroplated diamonds. Those portions of the wires immediatelysubjacent the working surface 20 function as the thermtlly conductiveportion of the heat-dissipating region.

FIGS. 6, 7 and 8 depict still another embodiment of this invention. Inthis embodiment, the wheel 26 is comprised of a number of layers ofperforated sheet 28 separated one from the other by spacers 34. In theparticular embodiment shown, the spacers 34 are an integral part of thesheet 28 and are formed when the sheets 28 are perforated. Other spacingmeans, such as wires or dimples formed into the sheets 28, might also beused. The wheel 26 has a working surface 32 comprised of an abrasivelayer 30. The respective sheets 28 are offset, one from the other, inthe radial direction, as best shown in FIGS. 7 and 8. Likewise, thelayers are also offset, one from the other, angularly with respect tothe central axis of the wheel, as best shown in FIG. 6. Offsetting ofthe respective layers insures a substantially continuous path for thecoolant flow from the center of the wheel toward the working surface 32,or at least through heat-dissipating regions immediately subjacent theworking surface. The perforation density (i.e., number of holes persquare inch), especially in the heat-dissipating region immediatelybelow the working surface 32, is dependent upon the amount of heat whichmust be removed from the workpiece-wheel interface. The perforationdensity and distribution shown in FIG. 6 is only illustrative and is notintended to indicate any particular critical configuration.

FIGS. 9, l0 and 11 show still further embodiments of tools made inaccordance with this invention. In FIG. 9, the entire wheel 38 iscomprised of an open-cell porous metal 40 (e.g., nickel) such asdescribed and claimed in copending U.S. patent application Ser. No.724,544 entitled Three Dimensional Electroformed Reticulated Latticeworkfiled in the names of Seymour Katz and Joseph L. Greene on Apr. 26,1968, and assigned to the assignee of the incident invention. Forpurposes of a more detailed description of the structure and propertiesof the aforesaid open cell porous metal, U.S. patent application Ser.No. 724,544 is intended to be herein incorporated by reference. Suchwheels have successfully contained 15% by volume nickel and had aporosity profile of about 45 cells per lineal inch. Extended heattransfer surface areas of about 75 inF/in. are obtained. A workingsurface 42 and resin support (not shown), like that disclosed inconjunction with FIGS. 3, 4 and 5, completes the wheel. A hub insert iscomprised of two parts 44 and 46. The two parts 44 and 46 are pressedinto the wheel from either side thereof and bonded thereto.

The FIG. wheel 48 is much like that of FIG. 9 in that it is comprisedprincipally of a porous metal 54. However, rather than being aperipheral wheel, the abrasive layer 50 which forms the wheels workingsurface 52 is on the face of the wheel 48. With the abrasive on theface, the tool can function as a sanding or polishing disc or the like.The particular contour or shape of the disc is such that the peripheraledge thereof is thinner than the body, hence providing a high degree offlexibility at the periphery of the wheel. This shape is well adapted tosanding and polishing operations. In this mode of operation, material isremoved from the workpiece under less severe conditions than under theconditions of peripheral wheel grinding and cutting where the wheels areinflexible, are forced into the workpiece, and have a comparativelysmall area of contact with the workpiece. It is at this small area wherethe tremendous heat is generated and must be quickly removed. Anotherstructural variation of this contour could be provided by forming awheel such as described in FIGS. 3-5 but by reducing the outsidediameter of the screen lamina progressively through the wheel from theworking surface to the back side of the disc. A hub 56 is bonded to thewheel in a convenient manner.

FIG. 11 is still another embodiment of my invention. In this particularembodiment, the heat-dissipating region 70 is shown as being completelydistinct from the central or body portoin 66 of the wheel 58. Theheat-dissipating region 70 is immediately below the porous abrasivelayer 72 which is working surface 74 of the wheel. The region 70 iscomprised of a porous metal of the type de' scribed. Virtually all ofthe heat which enters the wheel is removed in this short distanceradially inward of the Working surface 74. It is believed that adistance of no more than about inch is required to remove most of theheat (e.g., see FIG. 18). The bulk of the wheel, or central portion 66,may be comprised of any sufficiently strong material to withstand therigors of a grinding operation.- The lighter this material is, the lesspower is required to drive wheel. Materials such as metals and evencertain plastics, are acceptable to comprise the central portion 66. Inembodiments such as disclosed in FIG. 11, it is convenient to include aplurality of radial bores 68 in the central portion 66. The radial bores68 permit the introduction of the coolant into the hub area from whichit flows to the working surface 74. Depending on the precise nature ofthe operation being performed and/ or the equipment limitations of theuser, coolant may, of course, be introduced into the heat-dissipatingregion 70 by other means such as coolant jets (e.g., nozzle 43 of FIG.4) directed into the heat-dissipating region of the wheel from any of anumber of directions. This is true for all the wheels disclosed. Thevolume of coolant should be sufficient to convectively remove the heatproduced at the workpiece-wheel interface and conductively transmittedinto the heat-dissipating region of the wheel.

The following describes in more detail a specific example of a preferredembodiment, as well as a process for its manufacture. This embodiment isbest described in connection with FIGS. 3, 4 and 5. A wheel 14 which is7 inches in diameter and /2 inch wide is described. The individuallayers which form the wheel are comprised of No. 8 mesh copper screen.No. 8 mesh copper screen is woven from 0.028 inch copper wire andproduces an opening between the wires of about 0.097. Strips of thescreen are conveniently purchased in rolls. This screen strip is fedthrough a corrugating machine to crinkle the screen as best shown inFIG. 5. Corrugating or crinkling the screen provides several benefits.It provides a convenient means for spacing the many layers of screen,one from the other in the final stack or laminated structure. Thespacing provides a plurality of substantially continuous, relativelynontortuous passage from inside the wheel extending towards the workingsurface 20. The spacing also reduces the number of screen layers neededto make a wheel having a given thickness (i.e., /2 inch). This in turnreduces the mass of the wheel. As shown at A of FIG. 5, it is generallypreferred to corrugate the screen to an amount equal to about thethickness of the wires used in making the screen. From the corrugatedscreen, blanks of appropriate diameter are punched out. Simultaneously,a center hole is punched into each blank. The screens are next dustedwith a brazing powder. For copper screens, I prefer to use anickel-phosphorous brazing powder sold by Wall Colmonoy Corporationunder the name of Nicrobraz 10. An appropriate number of screens areassembled and stacked in a fixture for alignment and holding during thebrazing step. For the /2 inch wheel, about 17 layers of corrugatedscreen are required which produce an effective heat transfer surfacearea in the heat dissipating re ion of about 52 square inches per cubicinch (in. /in. of porous metal or laminated screen. The metal content ofthis porous region is about 36% by volume copper. The screens arerotated about the center of the wheel and with respect to each other toinsure a substantially uniform distribution of wires ends on theperiphery or working surface of the wheel. Likewise, the rota-tion ofthe screens provides a more tortuous flow path through the Wheel in theaxial direction than in the radial direction. This insures a betterradial flow of coolant. A weight is applied to the stack in the fixtureso as to press the respective layers close together during brazing toinsure a uniformly thick wheel. The stack is placed in a brazing furnaceand appropriately treated to bond the layers together. After the brazingoperatoin the wheel is prepared to receive a hub. The center hole isreinforced by impregnating an approximately one inch annulus about thecenter hole with a thermosetting liquid, such as Scottweld EC-2214. Thethermosetting liquid is then cured in accordance with the manufacturersinstructions. For Scottweld EC-2214, curing is accomplished by heatingfor 40 minutes at 250 C. A Teflon plug is preferably placed in thecenter hole to keep it clean and free of thermosetting liquid during thecasting and curing step thereof. After curing, the plug is removed andthe wheel hub hole is reamed to the desired hole size which, for a 7inch wheel, is preferably 1.25 inch. Subsequently, the wheel is trued toinsure its concentricity with the hub. Next, the wheel is cleaned, as bya vapor blast or fine standblast, to remove all small metal fragmentsfrom the wire ends, which may have developed during the trueing process.At this time, any necessary solvent degreasing of the wheel is alsoaccomplished. The wheel is appropriately masked to insure that only theworking portions of the wheel receive the electrocodeposited diamond.Many suitable masks or stop-off materials, such as waxes, lacquers,etc., are available to those skilled in the art. I generally prefer touse lacquers. After the lacquer has dried on the wheel, portions thereofare removed so plating can proceed where the lacquer has been removed.Lacquer removal is conveniently accomplished by means of a motor-drivenrotary wire brush. The diamonds are next plated onto the wheel. It isgeneral- 1y preferred to plate to a depth of about A; inch into theinterstices of the wheel. This is conveniently controlled by temporarilyplugging the balance of the pores with an inert filler such as wax orresin. It is preferred to use a nickeldiamond codeposition process,though clearly others such as copper-diamond, may also be used. Atypical codeposiion bath and its plating conditions are described below.

For plating the periphery of a wheel, the wheel is made the cathode inthe electrolytic codeposition bath. The bath is kept agitated, as by apropeller suspended in the solution, to keep the diamonds suspended inthe solution. Current density varies from 60 amp/ft. to amps/ft. duringthe plating cycle with closer control required near the end of the cycleafter the diamond deposit has increased. It is prefered that thethickness of the nickel deposit be greater than about 50% of the diamondmean diameter size but not greater than 100%. Better diamond retentionresults. After cleaning and removal of the masking and filler materials,the wheel is balanced.

Wheels made in accordance with the procedure recited above were testedby grinding a piece of KT silicon carbide ceramic. The test piece was atubular cylinder having an outside diameter of 5.788 inches, an insidediameter of 3.750 inches and a length of 1.625 inch. The silicon carbidehad a hardness rating of 13 on the Mohs scale. Grinding was performed onthe end across the diameter of the piece using water as a coolant. Thecoolant flowed through the heat dissipating region of the wheel at arate of about 0.22 gal./ min. The stock removal rate was 0.004 inch perpass of the wheel over the part for a total stock removal of 2.0 in. in42.3 min. A similar test was run on the same material using a commercialresin-bonded diamond wheel which removed only 0.001 inch per pass of thewheel and only 0.8 in. of stock in 6 hrs.

It appears that the superior performance of these wheels is the resultof a concerted interaction between conductive and convective heattransfer mechanisms in the working surface and the heat-dissipatingregion of the wheel. It has been observed that diamond wheels which wereotherwise substantially structurally identical but made of materialshaving different thermal conductivities performed differently withrespect to the amount of heat which was transmitted into the workpiece.The thermal conductivity of the material which comprised theheat-dissipating region in these wheels appeared to be a verysignificant variable. In this regard FIGS. 12-15 show that duringsustained grinding at constant wheel speed and coolant flow rate (air orwater), the amount of heat transmitted into the workpiece was generallyinversely proportional to the thermal conductivity of the materialcomprising the heat dissipating region of the wheel. For example, FIGS.12-15 show that porous heatdissipating regions comprised of coppertransmitted less heat into the workpiece than those comprised of nickel.FIGS. 12-15 further show that only the wheels of this invention coulddissipate the heat rapidly enough to permit accurate deeper cuts to betaken. This is true for both dry (air) and wet (water) test runs. Forexample, in the series of tests reflected by FIGS. 12 and 15 neither thesolid nor the resin-bonded wheels could withstand the thermal punishmentof deeper wheel feeds of a test block. In the FIGS. 12 and 13 tests, theporous wheels of this invention were /2 inch wide by 7 inches indiameter and were comprised of nickel and copper respectively withdiamonds plated on its working surface. The porous wheels each had ametal content of about 36% by volume metal and about 50 inI /in. of heattransfer surface area in the heat-dissipating region. The solid copperwheel had diamonds plated on its periphery and represented wheels havinga maximum conductive heat removal capability but a minimum of convectiveheat removal capability. The resin bonded wheel was of the commerciallyavailable D-120 P100 B% type in which the diamonds are held in a A; inchlayer of phenolic resin on an aluminum alloy wheel. The wheels weretested wet (water cooled) and dry (air cooled). The tests involvedgrinding stock off one of the 2 inch x 4 inch faces of a 1 inch x 2 inchx 4 inch sample blocks of GM46M tool steel heat treated to a hardness of60-62 R In the center of one 2 inch x 4 inch face a blind hole wasdrilled to within 0.025 inch from the opposite face (i.e., the face tobe ground). Constantan thermocouples were mounted in these holes. 0.001inch, 0.002 inch, and 0.003 inch cuts were taken as indicated by theadjustment on the advancing mechanism and the corresponding temperatureat each cut recorded. Actual stock removal was determined after eachseries of tests. The machine, which was a Do All wet and dry surfacegrinder, had an operating speed of 3400 rpm, a table translation rate of.38 cycles per minute, and a table cross feed of 0.020 inch per cycle.For the wet tests, water was used at a rate of 0.22 gallon per minute.Similar tests were conducted to determine the data reflected in FIGS. 14and 15, except that in these latter tests the thermocouples were placed0.062 inch from the surface being ground and the cutting was done in0.0005 inch increments between 0.0005 inch and 0.003 inch cuts. Becauseof the new location of the thermocouple, there was a downward shift ofthe temperatures recorded. Further, in the second test series the solidcopper wheel was provided with a nylon sleeve in the otherwise metal hubhole. This sleeve provided a slight protective cushioning effect notpresent in the first series of tests.

In the first dry test of the porous nickel wheel (FIG. 12), the wheelwas successively fed 0.001, 0.002 and 0.003 inch, respectively, into theblock in the manner indicated. When the block returned to roomtemperature, it was remeasured and found that a total of 0.0058 inchstock was removed as compared to the 0.006 inch wheel feed. Slight wheelwear was indicated which is normal for all grinding wheels during theirinitial use. The recorded temperatures are as plotted.

In the first dry test of the solid copper wheel (FIG. 12) the wheel wassuccessively fed 0.001, 0.002, and 0.003 inch, respectively, into theblock in the manner indicated. The actual stock removal as measuredafter cooling was 0.0057 inch. Like the nickel wheel, slight wheel wearwas indicated. The recorded temperatures are as plotted.

In the first dry test of the solod coper wheel (FIG. 12) the test wasterminated after the first 0.001 inch cut. The heat was generated sofast that the wheel grew radially and caused it to overcut more than the0.001 inch. Though wheel feed was only 0.001 inch, actual stock removalwas 0.003 inch. No meaningful correlation could be made between theapproximate stock removal and temperature since the difference betweenthe wheel feed and the actual stock removal was so great.

In the first dry test of resin bonded commercial wheels (FIG. 12) thetest was terminated after the first 0.001 inch cut. The heat generatedby the 0.001 inch cut caused the phenolic resin binder to decompose andrelease the diamonds from the bond. The actual metal removal was 0.0004inch.

In the first dry test of the solid copper wheel (FIG. 13), the wheel wassuccessively fed 0.001, 0.002 and 0.003 inch, respectively, into theblock in the manner indicated. The total stock removed was 0.0058 inchas compared to the total 0.006 inch wheel feed. The wheel showed signsof less wear than in the dry grinding test. The recorded temperaturesare as plotted.

In the first wet test of the porous copper wheel (FIG. 13), the wheelwas successively fed 0.001, 0.002 and 0.003 inch, respectively, into theblock in the manner indicated. The total stock removed was 0.0058 inchas compared to the total 0.006 inch wheel feed. The recordedtemperatures are as plotted.

In the first wet test of the solid copper wheel (FIG. 13), the wheel wassuccessively fed 0.001 and 0.002 inch, respectively, into the block inthe manner indicated. In this test the wheel grew radially and the testwas stopped after the second cut (0.002). In this test, when the wheelwas fed into the sample block 0.002 inch, the actual metal removed was0.0048 inch. The recorded temperatures were as plotted but no meaningfulcorrelation can be made between the temperature and the depth of cutowing to the complete loss of dimensional control.

In the first wet test of the resin bonded commercial wheel (FIG. 13) thewheel was fed 0.001 inch into the block in the manner indicated. In thistest the heat generated caused the phenolic bond to weaken and releasethe diamonds. The 0.001 inch wheel feed yielded only a 0.0006 inch stockremoval. Further, the heat genertated was more by way of friction thangrinding. The recorded temperature was as plotted, but no meaningfulcorrelation can be made between this temperature and the depth of cut.

In the second dry test of the porous nickel wheel (FIG. 14), the wheelwas successively fed 0.0005, 0.0010, 0.0015, 0.0020, 0.0025 and 0.0030inch, respectively, into the block in the manner indicated for a totalof 0.0105 inch and removed 0.0100 inch of stock. The recordedtemperatures were as plotted.

In the second dry test of the porous copper wheel (FIG. 14), the wheelwas successively fed 0.0005, 0.0010, 0.0015, 0.0020, 0.0025 and 0.0030inch, respectively, into the block in the manner indicated for a totalof 0.0105 inch. The actual stock removal was 0.0100 inch. The recordedtemperatures were as plotted.

In the second dry test of the solid copper wheel (FIG. 14), the wheelwas successively fed 0.0005, 0.0010,

0.0015, 0.0020, 0.0025 and 0.0030 inch, respectively, into i the blockin the manner indicated for a total of 0.0105 inch. The actual stockremoved was 0.0155 inch. The recorded temperatures were as plotted. Theinstallation of the aforementioned nylon bushing or sleeve allowed thesolid copper wheel to safely run through the entire test since the nylonapparently acted somewhat like a buffer and countered the effects of theradially growing wheel. However, like before, substantial overcuttingand loss of dimensional control was encountered and no meaningfulcorrelation can be made between the temperature and the depth of cut.

In the second dry test of the resin-bonded commercial wheel (FIG. 14),the wheel was successively fed 0.0005, 0.0010, 0.0015, 0.0020, 0.0025and 0.0030 inch, respectively, into the block in the manner indicatedfor a total of 0.0105 inch. The actual stock removal was 0.0035 whichindicated that the wheel was no longer effective and had broken downafter the 0.0015 inch cut. The recorded temperatures were as plotted.

In the second wettest of the porous nickel wheel (FIG. 15), the wheelwas successively fed 0.0005, 0.0010, 0.0015, 0.0020, 0.0025 and 0.0030inch into the block in the manner indicated for a total of 0.0105 inch.The actual stock removed was 0.0100 inch. The recorded temperatures wereas plotted.

In the second wet test of the porous copper wheel (FIG. 15) the wheelwas successively fed 0.0005, 0.0010, 0.0015, 0.0020, 0.0025 and 0.0030inch into the block in the manner indicated or a total of 0.0105 inch.Actual stock removal was 0.0095 inch. The recorded temperatures were asplotted.

In the second wet test of the solid copper wheel (FIG. 15 the wheel wassuccessively fed 0.0005, 0.0010, 0.0015, 0.0020, 0.0025 and 0.0030 inch,respectively, into the block in the manner indicated for a total of0.0105 inch. Actual stock removal was 0.018 inch. The recordedtemperatures were as plotted.

In the second wet test of the resin-bonded commercial wheel (FIG. 15),the wheel was successively fed 0.0005, 0.0010, 0.0015, 0.0020, 0.0025and 0.0030 inch, respectively, into the block in the manner indicatedfor a total of 0.0105. The actual stock removed was 0.0025 inch.Breakdown of the phenolic bond began at about the 0.001 inch cut.

As a result of these tests, it was concluded that during sustainedgrinding operations the solid copper wheels acted as heat sinks. Thesolid copper wheels initially removed considerable heat from the workingsurface of the wheel.

The workpiece itself also absorbed some of this heat. However, over anextended machining operation, the absorbed heat increased thetemperature of the wheel causing radial swelling thereof. This swellingcaused over-cut of the workpiece as well as established a potentiallydangerous situation in which either the spindle could be damaged, theworkpiece caused to fly off the table, or both. The use of the nylonbushing in the second series of tests reduced and hazard but alsointroduced another variable into the test. As the temperature in thesolid wheel increased, the heat removal rate into the wheel decreasedand the temperature of the workpiece rose. For the deeper wheel feedsvirtually all dimensional control was lost. It was reasoned that thisoccurred because the temperature difference, AT, between the workingsurface and the region subjacent that surface was continually decreasingthereby reducing the heat removal rate. Under sustained cuttingconditions the wheel grew rapidly and uncontrollably increased the depthof cut and caused overheating of the workpiece. With wheels made inaccordance with this invention, the diamonds are thermal conductors andthe dissipating region immediately below the working surface iscomprised of a material which has a relatively high thermalconductivity, a high porosity, and an adequate porosity profile forrapid heat removal. Wheels ofv this invention did not swell as do thesolid wheels. Rather the test results indicate that with wheels of thisinvention, increased cooling results from a rapid conductive removal ofheat from the workpiece via the diamonds and thermally conductive matrixforming the working surface and from the working surface via thethermally conductive heat dissipating region contiguous the workingsurface; that this heat is conducted deep (e.g. about M into theheat-dissipating region; and that therein a substantial amount ofconvective heat removal occurs incident to the extended heat transfersurface area in the heat-dissipating region. The tremendous heatgenerated at the point of contact between the diamond and the workpieceis rapidly transmitted through the thermally conductive diamond at ratesin excess of about 4(-+-dt/dx) per unit area of diamond incontradistinction to being insulated from the heat-dissipating region bya substantially less conductive abrasive particle such as A1203 or acarbide. Not only is a considerable amount of heat thus conductedthrough the particle but a cumulative benefit rate-wise is obtained byhaving the temperature of the metal in the heat-dissipating region keptlow resulting in a higher temperature gradient (dr/dx) between theworking surface and the heat-dissipating region. For purposes ofobtaining these benefits, it appears that not only should the abrasivesbe heat-conducting diamonds but also the matrix holding the particlesand the heat dissipating region should be comprised of materials havinga high thermal conductivity and that an extended heat transfer surfacearea should be provided in the heat-dissipating region to convectivelyremove the heat conductively transmitted into this region. Though, forthe heat-dissipating region, I prefer the use of copper which has athermal conductivity coefficient of about 0.9 g.-cal./(sec.)(cm. C./cm.) nickel, which has a thermal conductivity of about 0.14g.-cal./(sec.)(cm. C./cm.) has performed satisfactorily. Iron alloys,steels and alloy steels have conductivities not distant from nickel andare also acceptable materials of construction. Other alloys may also beused, but are usually not available in an acceptably porous form. Thealloyed materials frequently have thermal conductivities as low as 0.05g.-cal./sec.) (cm?) C./ cm.). I prefer electrodeposited matrices such asnickel or copper for bonding the diamonds but other metals and othermatrix forming techniques (e.g., sintering or brazing) may be used.

Other tests (FIGS. 16, 17) have shown that the amount of heat transfersurface area in the heat dissipating region is quite significant and islargely dependent on the nature of the coolant being used. In thisregard, FIG. 16 shows that when using a poor coolant, such as air, theinternal heat transfer surface is quite significant. If low workpiecetemperatures for deep cuts are to be obtained with aircooling, this areashould be at least about 40 in. of area per cubic inch ofheat-dissipating region and preferably about 50 in. /in. The family ofcurves shown in FIG. 16 represents the temperatures of a number ofidentical workpieces each cut at different depths with different copperscreen wheels. The depth of cut is shown for each curve. Thethermocouples were located 0.062 inch from the surface being cut. Theseveral wheels were substantially identical in all aspects except theinternal heat transfer surface area which was varied. In this regard,five 7 inch porous copper wheels (i.e., FIG. 3) were used. The firstwheel had a volumetric metal content of 38 percent and an internal heattransfer surface area of about 19 in.'-/in. of heat-dissipating region.The second wheel had a volumetric metal content of 34 percent and aninternal heat transfer surface area of about 42 in."/in. The third wheelhad a volumetric metal content of 37 percent and an internal heattransfer surface area of about 52 inF/infi. The fourth wheel had avolumetric metal content of 34 percent and an internal heat transfersurface area of about 89 inF/infi. The fifth wheel had a volumetricmetal content of 34 percent and an internal heat transfer surface areaof about 135 in. /in.

The results shown in FIG. 17 were determined in much the same manner asthose for FIG. 16, except that water was used as a coolant and flowedthrough the heat-dissipatrng regions at a rate of 0.22 gal/min. Thewheels used were the same. FIG. 17 shows that the workpiece will cutcooler with increased internal heat transfer surface areas. \Whencompared to FIG. 16, FIG. 17 further shows that, with an excellentcoolant such as water, the internal surface area requirements are lessstringent than when using lesser quality coolants, but that therenonetheless is a need for some convective outlet for the heat within theinterstices of the heat dissipating wheel. Though that outlet can beless for a wet-wheel than for a drywheel, it still must be substantiallymore than that provided by a solid-wheel (e.g., see dotted lineprojections). It is significant to note that the low surface area wheelshad large interstitial voids and used thick-wired screen which provideda working surface having large pockets of diamonds surrounded by largevoids rather than a more uniform distribution of diamonds and voidsfound when using smaller pored materials. The more uniform distributionprovides a better, more efficient heat dissipator.

Further benefits are obtained when the coolants are caused to impinge onthe workpiece at the diamond-work piece cutting interface so that thereis more convective heat removal right at the diamond-workpiece out wherethe temperatures are highest. More coolant, of course, increases thethermal benefits but may introduce a hydrodynamic variable into themachining operation which could be undesirable. Regardless, wheels ofthis invention are considerably more flexible with respect to thequality and quantity of coolant that can effectively be used in the deepcutting operations where heat generation has heretofore been theprincipal limiting factor.

Still further tests were conducted to determine the effectiveness of theheat removal mechanism in the wheels of this invention as compared tothat of a conventional commercially available resin-bonded wheel. Onesuch test is reflected in FIG. 18. The data reflected in the bar graphsof FIG. 18 was determined by placing thermocouples in each wheel atlocations 0.0625 inch, 0.250 inch and 0.500 inch radially inboard of theworking surface. A 0.0015 inch cut was then taken with each wheel andthe temperature within the wheel sensed. In the resin-bonded orcommercial wheel the temperature near the working surface was thegreatest. The wheel was progressively cooler at the 0.250 inch and 0.500inch depths as shown in FIG. 18. The five wheels made in accordance withthis invention, also shown in FIG. 18, showed very little temperaturedifference between the 0.062 inch depth and the 0.500 inch depth whichindicates the extremely effective heat removal capacity of these wheelsto remove the heat in the first inch of the heat-dissipating surface. Itis further noted that in all cases shown, the wheels of this inventionat the temperature-sensing strata ran substantially cooler than theresin-bonded commercial wheel at the /z-inch tempera- "cure-sensingstrata.

FIG. 19 reflects other data obtained and compares the workpiecetemperature (0.062 inch thermocouple depth) at different cutting depthswhen successive 0.0005, 0.0010 and 0.0015 cuts were taken with acommercial resinbonded wheel and a preferred wheel made in accordancewith this invention. This data shows that the resinbonded wheel couldnot withstand deeper cuts and accordingly the test was terminated afterthe 0.0015 cut. Regardless, FIG. 19 shows that the temperature of theworkpiece rose appreciably as the depth of cut was increased using theresin-bonded wheel but that with the wheel of this invention and atthese comparatively low cutting depths the workpiece temperature remainssubstantially constant at a temperature substantially below thatgenerated with the commercial wheel. Further, with the wet wheel,improved workpiece cooling results from high volumes of coolantthoroughly flooding the working surface from within the wheel to anextent not heretofore known. This form of flooding significantlyimproves the heat removal such that the wheels and the workpieces canwithstand much more rigorous and severe machining conditions.

A still further advantage is found in these wheels. In this regard, theporous layer beneath the working surface permits the metal chips removedfrom the workpiece to readily move into the voids and thereby precludesloading of the wheel which causes reduced cutting and generates moreheat than an unloaded wheel. While still in the voids, the heatcontained in the chips is readily removed, and as the wheel rotates outof contact with the workpiece the chips are flushed from the intersticesof the porous subsurface by the flowing coolant.

The entire wheel could be formed of the porous material which comprisesthe heat-dissipating region. That is to say, the heat-dissipatingportion can be an integral extension of the body portion. When theentire wheel is thusly formed, it has a relatively low mass. Because ofthe lower mass, less power is required to accelerate the wheel. Further,because of the improved cutting efliciencies the same jobs can beperformed at a power savings. Where power consumption and shippingweight are a major consideration, magnesium and aluminum are excellentcandidates for the heat dissipating region both because of theirlightness and because of their 0.4 and 0.5 g.-cal./ (sec.)(cm. C./cm.)thermal conductivity coefficients. Porous metal wheels have sufficientstructural integrity as to be considerably stronger than bonded orvitrified wheels, even at high rotational speeds. High speeds arepossible because the porous metal wheels have stronger bonds in relationto the overall low mass of the wheel. These higher rotational speedsresult in faster cutting rates. Higher rotational speeds, of course,tend to produce more heat. If this additional heat could not adequatelybe removed, then the improved speed capability would provide noadvantage. As indicated though, wheels of this invention actually doprovide an improved means for rapidly removing the heat generated,thereby avoiding excessive temperature buildup in both the wheel and theworkpiece. Accordingly, the wheel of this invention transcends the heatlimited infirmity of solid wheels.

Several other observations were made with respect to the operation ofthis wheel. First, and quite significantly, the diamond-platedembodiment of this wheel can be used quite satisfactorily in thegrinding of hardened steel or mild steel as well as carbides, ceramics,concrete, glass and plastics. Most manufacturers of present commerciallyavailable diamond-plated wheels nowcaution the user against the cuttingof steels, owing to the tendency of the wheel to load up resulting inthe ultimate loss of the wheel. For this reason, steel has commerciallybeen ground almost exclusively with alumina wheels. Still anotheradvantage noted with respect to the wheels of this invention is the factthat the porous nature of the heatdissipating region substantiallyreduces the formation of hydrodynamic films between the workpiece andthe wheel except at extremely high coolant flow rates. Thesehydrodynamic films, so common to solid and near solid wheels, reduce theeffectiveness of the wheels. The wheels of this invention are alsouseful for electrochemical machining wherein electrolyte flows throughthe wheel. However, the full mechanical cutting and heat-dissipatingcapabilities of my wheels are not completely utilized in the ECMenvironment since the bulk of the metal removal occurs by electrolytic,rather than mechanical action.

Cutting tools remove stock from a workpiece by a chip-producing process,in contradistinction to workpiece erosion by friction technicallycharacteristic only of grinding tools. Regardless, many diamond toolsare frequently called grinders when, in fact, they are chip producersand accordingly might better be classed as abrasive cutting tools.Since, however, the industry apparently does not make this distinctionand has adhered to the misnomer grinder, it is herein intended that theterm grinding be interpreted in the same sense as it has been acceptedin the industry. Accordingly, the word grinding is considered to bedescriptive of a stock removal process involving a single or a series ofsmall cuts taken in a workpiece with a plurality of abrasives and isintended to include such functions as are normally accomplished by suchtools as surface grinders, abrasive cut-off wheels, abrasive saws, etc.

While this invention has been described solely in terms of certainspecific embodiments thereof, I do not intend to be limited thereto butrather only to the extent defined hereafter.

I claim:

1. A method of making a highly porous laminated cutting wheel having aworking surface on its circumferential periphery and a heat-dissipatingmetal region contiguous- 1y underlying said working surface, said heatdissipating metal region having a thermal conductivity of at least about0.05 g.-cal./ (sec.) (cm?) C./cm.) and being sulficiently porous topermit macro-volume flow of coolant therethrough and out said workingsurface, comprising the steps of: pressing a plurality of discreteporous metal discs together into a compact stack of said discs eachface-to-face and contiguous the next adjacent disc in said stack;metal-bonding the faces of each disc to the faces of the next adjacentdiscs to unite said discs one to the other without substantiallyaffecting their porosity and to thereby form a porous laminate of saidmetal discs, said laminate having a circumferential peripheral surfaceportion formed by the peripheral edges of said discs; and securing alayer of diamonds in a metal matrix to said circumferential surfaceportion to form said working surface without substantially plugging thepores of said laminate immediately subjacent said surface.

2. The method according to claim 1 wherein said discs comprise wirescreens and including the steps of corrugating said screens prior tosaid stacking.

References Cited UNITED STATES PATENTS 2,376,254 5/ 1945 Humphrey et al.51-309 3,377,150 4/1968 Corley 51293 2,290,631 7/1942 Buchmann 513092,361,492 10/1944 Pare 51309 DONALD J. ARNOLD, Primary Examiner U.S. Cl.X.R. 5 13 09 UNITED STATES ATENT OFFIIQE CERTIFIC OF EQTEUN Patent No.3,813,230 Dated M 28, 1974- Inventorg's) Karol W Ferchld I It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby maltreated as shown belew;

F Col 1, line 42, eftem' "In." and becimse "gmier" We the C01 2, lineZ216, 1 1 Ctolumn '3, line 15, "eeetienal" enemies? be m: sectioned line32, the werd *wheeels eheulfl be m wheels 43,

;? Flt? 9" should be mm FIG 19 Calm line 3. "thieknes" ehmald bethickneee line 2? thersmtlly should be thermally (2011mm 5, line 27pertein should read portion line} 39, after drive en fi befiezse "'wheelinsert we the celuwmfiie line 20, "wiree" eh euld be wixe line 29;,"operatoin" elwuld be eperetien line 36, delete "Co" after 25 0'" andinsert F line 38,, "step ehoulfi be ekeps line 43, "etanleefl eheuli besenlest C011 7, line the femmula reading "60 o/fe eheuld be 60 amps./t.line 19, "Mohs" sheuld be Mobs filelumn 8, line 20', "nylon" ehoulfl beNylen line 32, delete 'selid and insert; porcme line 3%, fielete "soledcaper" and insert. solid copper -r line 54, delete my and ineexsiz; wwet and delete eelid copper d ineert porous nickel "0 Celumn 9, line 8,genextated' shmalfl; he we generated line 31, "nylon" should! be Nylonline 33, 'nylen" should be Nylezn line 56, "er" shmzld be fer Col 10,line 8,, "nylon" shoulfi' be Nylon -=--s lime delete "d" and ineerk theColumn 14, line 28;, (In the Claims) steps" shawl be step e Signed andsealed this 19th day eflflcverriber 197 4 e (SEAL) Attest:

MeCOY 1' 1. GIBSON JR. ca MARSHALL DANN Attest1ng Officer ICorm'n'lssiuner of Patents

